A Francis turbine is used in a hydraulic machine, including a reversible pump-turbine, for power generation.
A conventional Francis turbine runner is described in U.S. Pat. No. 4,479,757. This conventional Francis turbine runner includes blades whose inlet (a leading edge) shape is curved toward a direction opposite to a rotating direction of a turbine operation from a band side to a crown side.
Another conventional Francis turbine runner is described in U.S. Pat. No. 6,135,716. This conventional Francis turbine runner includes blades whose inlet (a leading edge) shape is curved toward a rotating direction of a turbine operation from a band side to a crown side. This conventional Francis turbine runner also includes blades whose outlet (a trailing edge) shape is curved toward a rotating direction of a turbine operation from a crown side to a band side.
Also, a conventional reversible pump-turbine is described in Japanese Patent Publication (Kokai) No. 8-312517. A runner of this conventional reversible pump-turbine has blades whose trailing edge is curved toward a direction opposite to a rotation direction of turbine operation from a middle point of the trailing edge to a band side. Also, this conventional runner has a trailing edge, whose profile projected on a meridian plane (a plane including rotation axis) is elongated toward a downstream side at a band side to improve hydraulic efficiency in a condition of a partial load operation.
Another conventional reversible turbine is described in Japanese Patent Publication (Kokai) No. 2000-136766. A runner of this conventional reversible pump-turbine has blades whose trailing edge is curved so that the trailing edge is formed to be convex in a rotation direction of a turbine operation.
Those shapes of the blades of conventional Francis turbines are developed to improve a hydraulic efficiency or to reduce cavitations. Still there is room to develop the shape of the blades that improves the efficiency because of the recent development of technology in a field such as computational fluid dynamics.
Especially, it is known that secondary flow, which is a flow not being along a flow line, distorts a pressure distribution on the blades and results in loss of hydraulic efficiency.